According to the invention there is provided a relatively simple, economically viable device for "time sharing" a single source of electrical power between a predetermined number of loads, such as automotive heating accessories, with a view to obtaining adequate utility from each of the loads by powering each for ambient temperature-related variable time blocks, while avoiding the risk of overloading the power source, a condition which may occur should a number of accessories be in operation simultaneously.
By way of background to the subject matter of the present invention, as related to the automobile application, it is well known that certain areas of the world experience severe weather conditions for part, or all of the calendar year. A number of automotive accessories have been developed to maximize the probability of engine starting and to provide some degree of utility and comfort to the operator by heating or cooling the interior of the automobile while not in service.
Dealing firstly with the problem of starting an extremely cold engine, the most notable development includes an immersible electric coil type heater which is mounted in the engine block in such a manner so as to continually heat the engine cooling fluid and consequently the entire engine block. An engine block heated in this manner when not in operation, will start more readily in extremely cold weather due to the lower viscosity of the heated engine lubricants. Additionally, highly efficient battery chargers have been developed which ensure maximum power from the battery when starting in cold weather, recognizing that power capability of an electrical battery drops off appreciably as a function of declining temperature. Alternatively, battery heaters or "blankets" have been designed which maintain the battery temperature, and therefore power, at a high level when the automobile is not in use.
Numerous types of in-car space heaters have been designed to be accommodated within the car to provide the operator with some degree of comfort. These heaters usually consist of an electrical resistance coil to provide a heat source coupled with an air circulating fan to ensure even distribution of heated air throughout the car interior. It should be noted that this device not only provides the required comfort in very cold weather, but also either prevents a build-up of frost on the exterior of the vehicle windows, or at least eases the effort with which this frost may be removed in order to ensure adequate visibility. Finally, in climates experiencing high temperatures, independent air-conditioning equipment has also been adapted for inclusion within vehicles for the purpose of maintaining an even and bearable temperature level.
In order to power the above described electrical accessories, all of which are only operated when the vehicle itself is not in operation, it has become a practice in these geographic regions to provide an electrical power source wherever vehicles are parked for any appreciable period of time, whether at the home, office, factory, or even public parking lots. In an increasing number of cases, these electrical power sources occur with a number of power plugs wired in parallel, thus limiting the electrical load that should be placed on any one power plug. For example, in a public parking lot, it is general to find four plugs wired in parallel to a thirty-five amp main circuit breaker, thus limiting the average maximum load on each of the five plugs to 8:75 amps. Considering the power requirements of various automotive electrical accessories described heretofore, it is obvious that the combined series of plugs could be automatically tripped-out should a number of the plugs be subject to a load exceeding 9 amps, such that the total load at a main breaker exceeds 35 amps. To illustrate the problem further, a conventional automotive block heater of the immersion coil type, uses 600 watts of power, which at 110 volts draws current at the rate of 5.5 amps. An in-car heater typically uses 850 watts of power, causing a 7.72 amp draw at 110 volts. Therefore, it is common to note signs in parking lots warning the operator that the electric circuits are designed to power only engine block heaters, and that in-car heaters are not to be operated in addition to the engine heaters under any conditions, for fear of overloading the entire circuit and causing a great deal of inconvenience to other operators.
Particularly recognizing the above mentioned limitations of outdoor electrical parking facilities, on the one hand and the ever present desire of an operator to install and operate electrical automotive accessories which either improve the cold weather starting capability of the engine or provide some degree of creature comfort, it is the essence of this invention that means be provided whereby utility, comfort, and the power draw limitations of individual car plugs are automatically balanced so that each requirement or limitation is satisfied to a reasonable degree.
From one aspect the invention provides an electrical power sharing device comprising a single power inlet feeding two power outlets alternately for periods of time determined by the ambient temperature, said device comprising a bimetallic strip contacting the profile of a continuously rotating cam and opening and closing the electrical connections between the power inlet and the power outlets during each revolution of the cam for periods determined by the profile of the cam and the curvature of the bimetallic strip as determined by the ambient temperature.
From another aspect, the invention provides an electrical power sharing device comprising a single power inlet and two power outlets, a cam rotated continuously while power is supplied to said inlet, and a temperature responsive device including a part contacting the profile of said cam and an electrical contact adapted to contact one or the other of two contact members to connect said power inlet alternately to one or the other of said outlets, the profile of said cam being such that one of said contacts is closed for part of each revolution of the cam whilst the other is closed during the remaining part of such revolution, the ratio of said parts being determined by the position of said temperature responsive device in relation to the cam.
From yet another aspect, the invention provides an electrical power sharing device comprising a single power inlet and two power outlets, a cam rotated continuously while power is supplied to said inlet, the cam being mounted eccentrically to provide maximum and minimum lifts for a cam follower during varying proportions of a revolution of the cam. The cam follower includes a metallic strip, an electrical contact carried by said bimetallic strip connecting one of said outlets to the inlet during the period of maximum lift and the other of said outlets during the period of minimum lift.
In this age of increasing awareness of the necessity to conserve power, the present invention has the added advantage of providing a means of powering more than one electrical load, while causing only a marginal increase in the power consumption incurred when powering only one such load.
For example if a 600 watt block heater is powered 100% of the time, an average power draw of 5.5 amps occurs. However, with the proposed power sharing device described herein, the power is cycled from one circuit to the other, dependent upon ambient temperature so that, for example, at -6.degree. C. the present invention automatically powers the block heater 60% of the time (with a power draw of 5.5 amps), and an 850 watt in-car heater 40% of the time (with a power draw of 7.72 amps), resulting in an average power draw of only 6.38 amps.
Further, overall power consumption can be reduced by incorporating a means of shutting power off to both output plugs above a giver temperature.
In essence, the electrical power sharing device to be described in more detail hereinafter, accomplishes in a simple and economic manner, the "sharing" of one power source alternately to each of the two output power plugs incorporated into the same apparatus, said sharing to be automatic and proportionate to the ambient temperature in the cabin of the automobile.
The variability of the time "on" and "off" ranges within an approximate 12-15 minute time cycle, resulting from the incorporation into the apparatus of a bimetallic "temperature sensitive" element running on an eccentrically mounted cam in such a manner that the automobile heating accessories most important to the starting of an engine in extremely cold weather are powered 100% of the cycle (that it, continuously) as the temperature in the cabin of the automobile drops below -10.degree. C. (signifying a drop in outside temperature). As the cabin temperature will normally be comfortable, and the engine block hot when the unit is first plugged in, it is advantageous to design the bimetallic contact arm/cam shaft combination in such a manner that the in-car heater is powered only as the cabin temperature drops below +5.degree. C.
In the preferred embodiment shown in the drawings and described hereinafter, the device is designed for the distribution of the main voltage (eg 100 v or 250 v) power source in the time percentage ranges shown in Table 1:
TABLE 1 __________________________________________________________________________ -10.degree. C. +5.degree. C. Temp or below -7 -5 -3 0.degree. C. +1 +2 +3 +4 and above __________________________________________________________________________ Plug 1 On % 100% 70% 50% 30% 0% 0% 0% 0% 0% 0% Plug 2 On % 0% 30% 50% 70% 100% 80% 60% 40% 20% 0% __________________________________________________________________________
The preferred grouping of the automotive accessories would be:
______________________________________ On Plug #1: (a) an automotive engine block heater or ram pump OR (a) an automotive engine block heater or ram pump in conjuntion with either: (b) a light duty battery charger OR (c) an electric battery blanket (heater) On Plug #2: (d) an in-car space heater commonly utilizing an electric heating coil and an electric circulating fan. ______________________________________
In sharing, or cycling the input power to each of the two groups of electrical accessories described above, it is specifically claimed that an appreciable and beneficial portion of the ultimate utility of each of the driven accessories is achieved while ensuring that the source power circuit is not overloaded and subsequently "tripped" out. This high degree of utility is achieved by virtue of the fact that in the case of accessory (a), the block heater, accessory (c) the battery blanket and accessory (d), the in-car heater, the mass of the engine block, the engine coolant, the battery, the air and interior components of the automobile all act as "heat sinks" to varying degrees, and therefore store and evenly distribute the input energy (i.e. heat), in such a manner as to accomplish a respectable and adequate utility of each of the accessories.
The specific object of not exceeding the recommended load for a specific plug in a parking area where a number of car plugs are wired in parallel (with a limiting amperage rating of for example, 8 to 10 amps per plug) is accomplished by limiting the total amperage draw on each of the output plugs of the device, by grouping the powered accessories in such a manner that their combined amperage draw does not exceed the limit of the specific parking lot plug, and by ensuring that only one plug of the device (and therefore only one grouping of accessories) is powered at any one coment in time.
To further illustrate this feature, the following typical combination of accessories is exemplified:
Output Plug No. 1: --powering the following:
(a) engine block heater 600 watts--5.5 amps PA1 (b) battery charger--ranging from 4 amps maximum loading on a dead battery to 0.8 amps on a charged battery and assuming an average draw of 1.2 amps on a normal in-service battery. PA1 (a) an in-car heater--850 watts--7.72 amps
Output Plug No. 2: --powering the following:
Under these accessory combinations, output Plug No. 1 will draw an average of 6.7 amps while output plug No. 2 will draw 7.72 amps, thus ensuring that the input power source is never overloaded and the probability of an automatic electrical "trip-out" of a group of parking plugs is minimized.
It therefore naturally follows that while achieving a good portion of the ultimate utility of the various accessories, the total power consumption is appreciably reduced. That is, taking the above example of accessories (a), (b), and (d), if all were powered simultaneously, a total amperage draw of 6.7+7/72=14.42 amps would result. By utilizing the invention, at for example an automobile interior temperature of approximately -6.degree. C., whereby accessories (a) and (b) would be powered for 60% of the cam cycle, then accessory (d) would be powered for 40% of the cam cycle, average amperage draw of (6.7+0.6)+(7.72+4)=7.10 amps would result, thus halving the power consumption with only marginal loss of utility.